This application claims the priority benefit of Taiwan application serial no. 89103353, filed Feb. 25, 2000.
1. Field of Invention
The present invention relates to a method for compensating digital signal. More particularly, the present invention relates to a method for compensating the digital signal produced by a high speed of optical storage device.
2. Description of Related Art
Due to the rapid development of multimedia systems, optical storage device has become standard equipment in personal computers. To process ever-increasing quantities of image and audio data, rotating speed of the optical storage device has gone up tremendously. In general, part of the error signal from an optical device comes from the rotating frequency signal of the motor. When the optical disk spins fast, magnitude resulting from side effects also increases significantly. Hence, the error signal must be compensated properly.
FIG. 1 is a block diagram showing the architecture of a conventional focus and track servo system. The focus and track servo system includes an optical sensor 10, a signal pre-amplifier 12, a compensator 14, a power amplifier 16 and an actuator and lens module 18. The optical sensor 10 picks up focus error (FE) signal and lens position signal fed back from the lens of the optical pickup head to generate a plurality of signals to the signal pre-amplifier 12. Output signal from the signal pre-amplifier 12 is combined with the disk wobble and vibration signal before feeding into the compensator 14. Signal compensation is conducted inside the compensator 14. The compensated signal is transferred to the power amplifier 16, for amplification. The amplified signal is then transferred to the actuator and lens module 18 for producing lens position signal that drives the optical pickup head.
In general, error signal is compensated by a lead compensator and a lag compensator. Typically, the lead compensator is a differentiator circuit such as a high frequency filter capable of stabilizing any input signal. In contrast, the lag compensator is an integrator circuit capable of lowering the steady state error of low frequency signals.
FIGS. 2A and 2B are two different conventional lead-lag compensator architectures. FIG. 2A is a block diagram of a serially connected lead-lag compensator while FIG. 2B is a block diagram of a parallel-connected lead-lag compensator. As shown in FIG. 2A, the error signal is input into a lead compensator 20 and then a lag compensator 22. The output signal from the lag compensator 22 is passed to a power amplifier and then transferred to an actuator 24. On the other hand, as shown in FIG. 2B, the error signal is sent to a lead compensator 20xe2x80x2 and a lag compensator 22xe2x80x2 concurrently. Output signals from the lead compensator 20xe2x80x2 and the lag compensator 22xe2x80x2 are summed before passing to a power amplifier. output signal from the power amplifier is transferred to an actuator 24xe2x80x2.
As the rotating speed of an optical storage device increases, problems caused by insufficient bandwidth are more serious. Because the motor turns very fast, the rotating frequency may be too high for the lag compensator. Hence, when the aforementioned architectures are used to compensate for the error signal, the lead compensator and the lag compensator can hardly lower the steady state error at rotating frequency (the rotating frequency of the spindle motor for driving the optical storage device).
In addition, due to the high rotating frequency of the driving motor and the non-overlapping of amplified frequency bandwidths between the lead compensator and the lag compensator, suitable compensation is difficult to generate.
In the design of actuator for an optical disk system, secondary resonance problem may persist. Consequently, the lead compensator may be limited by second resonance, resulting in the inability to produce higher amplification of frequency and magnitude by the lead compensator. With a poor lead compensator design, a high frequency noise may be produced by the actuator. In the meantime, since the lead compensator can only amplify localized frequency, frequency bandwidth from the lag compensator may be compressed. Hence, conventional lead-lead compensator architecture can hardly meet the specification of optical device, especially in high speed optical storage device.
Accordingly, one object of the present invention is to provide a signal compensation device for a high-speed optical storage device capable of processing the error signal at the high-speed rotating frequency.
A second object of this invention is to provide a signal compensation device for a high-speed optical disk system capable of processing the error signal at high-speed rotating frequency portion so that stead state error within the error signal is lowered.
A third object of this invention is to provide a signal compensation device for a high-speed optical disk system capable of processing the error signal at high-speed rotating frequency portion so that stead state error within the error signal is lowered, wherein the high-speed rotating frequency portion of the signal is processed by a bandpass filter.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a signal-compensating device for an optical storage device. The compensation device includes a lead compensator, a lag compensator, and a bandpass filter. The lead compensator picks up error signal from the optical system. The lag compensator is connected to the lead compensator for receiving signal from the lead compensator. The bandpass filter (BPF) also picks up error signal from the optical system and then amplifies the rotating frequency portion of the error signal. Finally, signal generated by the lag compensator and the amplified signal produced by the bandpass filter is summed and then transferred to the actuator of the optical system, thereby lowering stead state error of the error signal. Since the rotating frequency portion of the error signal is processed by a bandpass filter, problems generally associated with a conventional optical system due to insufficient frequency bandwidth are eliminated.
The invention provides an alternative signal-compensating device for an optical storage device. The compensation device includes a lead compensator, a lag compensator, and a bandpass filter. The lead compensator picks up an error signal from the optical system to produce a first output signal. Similarly, the lag compensator picks up the error signal from the optical system to produce a second output signal. The bandpass filter picks up the error signal from the optical system and amplifies the rotating frequency portion of the error signal to produce a third output signal. The first, the second and the third output signals are summed to produce a resulting signal. Finally, the summed signal is transferred to the actuator of the optical system. The rotating frequency portion of the error signal is processed by a bandpass filter. Hence, problems generally associated with a conventional optical system due to insufficient frequency bandwidth are eliminated.
This invention also provides a method for compensating the signal of an optical storage device. Error signal produced by the optical storage device is fed to a lead compensator, a lag compensator and a bandpass filter. The bandpass filter processes the error signal in the rotating frequency portion. Output signals from the lead compensator, the lag compensator, and the bandpass filter are summed into a compensated error signal for lowing a steady state error of the error signal
This invention also provides another method for compensating the signal of an optical storage device. Error signal produced by the optical storage device is fed to a lead compensator and a bandpass filter. The bandpass filter processes the error signal in the rotating frequency portion and thereby generates a filtered error signal. Output signal from the lead compensator is fed to a lag compensator, whereby a lead-lag compensated error signal is generated. The filtered error signal and the lead-lag compensated error signal are summed into a compensated error signal for lowing a steady state error of the error signal.
In the above method, the error signal fed into the compensator can pass sequentially through a lead compensator and then a lag compensator for signal compensation. Alternatively, the error signal fed into the compensator can be diverted to the lead compensator and the lag compensator for signal compensation simultaneously and then summed to produce an output from the compensator. The method utilizes the bandpass filter to process the high-speed rotating frequency portion of the error signal. Hence, problems generally associated with a conventional optical system due to insufficient frequency bandwidth are eliminated.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.